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Wednesday, November 24, 2010

One of the most beautiful species of thread-waisted wasps is Ammophila aberti, found commonly here in southern Arizona. It actually ranges throughout western North America, east as far as Iowa, and south into Mexico. These sleek, silvery wasps are a little larger than the average Ammophila, approaching the length of A. procera, but not nearly as robust.

I was fortunate enough to come across a fairly large nesting aggregation of this species at Ft. Lowell Park in east Tucson on May 11, 2009. The female wasps were digging in a very flat area with hard, baked soil. They would literally take bites out of the earth in order to excavate their nests. Despite the abundance of wasps, it was still a challenge to get images of them. The wasps would dig a bit, fly up, settle again, and repeat the process. Consequently, I had many images with no wasp in sight!

It turns out that the nesting behavior of Ammophila aberti has been well documented. One study revealed that females may initiate more than one nest at a time. Some had simultaneously started eight different burrows, up to a dozen for one ambitious specimen. Few of the nests were finished, however. Could they be creating “dummy” nests designed to confuse parasites like velvet ants that will dig open the nests of their hosts? That would be an ingenious ploy if so.

It may also take a female wasp a long time to furnish food for its offspring. A single egg is laid on the first caterpillar to be stored in the cell at the end of the vertical or angled burrow. By the time the last caterpillar is hunted, the larva from that egg may be reaching maturity. This has been interpreted by some researchers as progressive or “delayed” provisioning, feeding the larva as it develops, but clearly this is not the case. It may simply take some female wasps longer to find a full complement of caterpillars. Also, prolonged inclement weather may delay hunting activities for the females. Lastly, temporary scarcity of prey may delay the ability of the females to find caterpillars.

Ammophila aberti might be considered something of a generalist in that it uses a wide variety of Lepidoptera species in provisioning its nests. The study cited above recorded caterpillars from five different families of moths and butterflies (and skippers) used by this wasp: Geometridae, Noctuidae, Pyralidae, Hesperiidae, and Pieridae. An average of about six caterpillars per nest was the norm for the Colorado study of this species.

Another trait exhibited by this species is prey-stealing from other wasps in the nesting aggregation. A female returning to her nest is vulnerable to robbery since she must put down her caterpillar catch to open the temporary plug on her burrow. She may be attacked by one or more others of her kind that try to wrest the caterpillar from her. The hijacking is frequently successful. Further, some wasps may actually dig open the nest of another wasp and pilfer the paralyzed cache, though this is a rarer phenomenon.

As is the case with most other fossorial (burrowing) wasps, satellite flies (Sarcophagidae: Miltogramminae) are a constant threat to parasitize the nest. Interestingly, I observed another potential parasite in the form of a bee fly, Thyridanthrax sp. The female flies were hovering over the open nests of the wasps, lobbing eggs down into the tunnels in the manner of a jet bomber. Thanks to Joel Kits for making the identification from the above image, originally published on Bugguide.net.

Clearly, there is still much to be learned about this, and the vast majority of other species of solitary wasps. So, next summer, resolve to get out and make your own observations. You are almost guaranteed of making groundbreaking contributions to our collective knowledge. Meanwhile, have a very happy Thanksgiving holiday. Good luck provisioning your table with things more appetizing (and hearty) than caterpillars 

Wednesday, November 17, 2010

One of the most common, and most handsome members of the genus Ammophila east of the Rockies (and south to Mexico City) is A. pictipennis. It is black in color, with red on the abdomen, and the black areas have metallic blue reflections in the right light. The wings are orange or yellow. The orange wings and lack of any silver bars on the side of the thorax help identify the species easily.

The individual above was imaged in Ocean City, New Jersey, fairly early on an overcast morning (October 19, 2010). It is in the classic “sleeping” posture adopted by Ammophila wasps during the night and inclement weather. The wasps grip a stem with their jaws, and prop their bodies at about a forty-five degree angle with their second and third pairs of legs. They often roost in loose clusters, jockeying for the best locations before settling down. This seems like odd behavior for supposedly solitary wasps. I once found a tight cluster of several Ammophila at Smith Rock State Park in Oregon. I initially thought it was a cluster of seeds or berries drooping from a short, erect plant.

When not resting, a female A. pictipennis is a busy insect. The species usually nests in sand, but will also excavate its shallow, vertical or nearly vertical burrow in hard-baked soil. The shaft is barely longer than the wasp herself, but ends in a nearly perpendicular cell that is spacious enough to accommodate the wasp and a lone caterpillar host. The specimen below was imaged at the Orange Airport in Orange, Massachusetts, September 7, 2009. She had brought a caterpillar to the vicinity of the burrow and was preparing to open it.

Known host caterpillars used by this species include mostly cutworms like the Armyworm, Mythimna unipucta, the Spotted Cutworm, Xestia c-nigrum, the Yellow-striped Armyworm, Spodoptera ornithogalli, and the Corn Earworm, Helicoverpa zea. There is at least one record of a caterpillar of the Common Sootywing (a skipper), Pholisora Catullus being used as prey.

Image above courtesy of Giff Beaton

The nesting behavior of this species is covered in detail by Phil and Nellie Rau in Wasp Studies Afield (Princeton University Press, 1918). Their interpretation of the wasps reveals at times perhaps more about the human observers than the reality of the instinctive processes going on in the insects. Still, it makes captivating reading and creates a real appreciation for the toiling labor of these creatures, as in the process of closing a nest:

”In her next selection she seems to be more particular. She goes here and yonder, pausing at clods and tiny pebbles, sometimes lifting them or turning them over. When finally she finds one that suits her fancy…she brings it in her mandibles and, grasping it firmly, she rubs, pounds and hammers down the dirt on the top of the hole until all traces of the fill are obliterated. When she has finished, we ourselves cannot discern the spot. Her task, so skillfully done, is now at an end; she throws her tool aside a few inches and flits away with an utterly careless air, as if she had forgotten all interest whatsoever in this place – and quite possibly she has. It is interesting to note that she cannot be persuaded to use this tool before the precise time for it. Once we tossed her a tiny pebble while she was yet busy grinding to pieces her clods with a pestle-and-mortar motion, but she only took it, without ado, and laid it back on her rubbish-heap, where an annoying bit of stick and a troublesome cinder had already been placed. Later on, when she was ready for her hammer, she went directly and, to our great delight, got our pebble which she had so stolidly spurned only a few minutes before….”

The image of an ungrateful hymenopteran is at least slightly amusing.

Subsequent research has shown that the “tool use” is simply the culmination of a series of instinctive behaviors. Still, one has to wonder if there was an individual “smart” wasp that increased the survival chances of her offspring by securing the closure of the nest burrow more thoroughly in this manner. Certainly, velvet ants are expert at detecting the subterranean nests of their hosts and digging them open, so such parasites must exert strong evolutionary pressure on the wasps to prevent break-ins.

A little more technical information is available on this page from Discover Life; and once again Dick Walton provides a wonderful online video that highlights the differences in nest excavation between A. pictipennis and A. procera. See if you can make your own observations of these fascinating species.

Monday, November 15, 2010

In the nearly two years I have been taking digital images of insects, I have managed to capture, largely be accident, a few insects in flight. The resulting images reveal that insects are far from fragile, but definitely agile.

For every shot I get of an insect winging its way out of the picture frame, I get at least as many of flower without fly, or rock without wasp, the perches long since vacated by the insects, if that only means by a millisecond. And that happens when I’m trying to capture an image of a stationary insect!

unidentified fly

I can’t imagine trying to capture insects in flight on purpose, but that is exactly what some photographers have been able to do regularly. Stephen Dalton, and English naturalist and photographer, was perhaps the first to successfully document different insects in flight. His book Borne on the Wind (Reader’s Digest Press, 1975) remains a classic. Another Englishman, Dr. John Brakenbury, published Insects in Flight in 1992 (Blandford, a Cassell Imprint). Both men achieved their success under largely controlled circumstances, rather than outdoors in “the wild.” Still, the resulting images are breathtaking, and highly informative about the physics of insect flight.

I’m happy to simply communicate the fact that some insects *can* fly. Many people are unaware that most beetles can fly, so having an image like this one of a blister beetle (Lytta auriculata) taking off is helpful in illustrating that beneath its wing covers a beetle has membranous wings it uses to fly.

Sometimes I can even capture courtship behavior, like between these two Golden Longwing butterflies, Heliconius hecale, native to Central America but performing locally in “Butterfly Magic” at the Tucson Botanical Gardens.

Here, the male is making hovering overtures to a female that is unreceptive. She signals this by essentially mooning him. Yeah, I used to get that a lot, too, dude….

Most of the time, I get images of insects arriving at, or departing from, a flower, or other perch. Here are a few examples:

Eumenes bollii potter wasp

Villa bee fly

Ammophila thread-waisted wasp

Insects are the undisputed evolutionary pioneers of animal flight, so it should come as no surprise that they are masters of aerial maneuvering, speed (at least for their size), and durability. Even the butterflies banging their way around indoor butterfly exhibits are barely slowed down despite what one might consider devastating damage to their wings.

We stand to prosper by continuing research into insect flight. How can a dragonfly manufacture turbulence, something deadly to a fixed-winged aircraft, and then use that turbulence to generate lift? Imagine the possibilities if we could duplicate the intricacies of insect wing movements in our own planes and helicopters. Maybe we, ourselves, could ultimately float like a butterfly….

Wednesday, November 10, 2010

It probably became apparent several postings ago that the vast majority of insects have no “common name” in English. Today’s featured species, Ammophila femurrubra, is no exception. In fact, information on this handsome wasp seems to be lacking as well.

Little in the way of research funds and scientific attention is lavished on most insects unless they are of economic importance (read “pests”). You could argue that Ammophila thread-waisted wasps that prey on caterpillars in agricultural settings actually *are* economically important, but in a good way. Most administrators and bureaucrats that dole out research dollars don’t seem to be convinced, however. Consequently, any observations and documentation on such solitary wasps is usually executed voluntarily by “amateur entomologists” that in today’s language we call “citizen scientists.”

Chief among the pioneers to illuminate the biology of solitary wasps were George and Elizabeth Peckham, whose ground-breaking work Wasps, Social and Solitary (Archibald Constable and Company, Ltd., 1905) set the standard for their American followers. Phil and Nellie Rau, who published Wasp Studies Afield in 1918 (Princeton University Press), continued the Peckham’s legacy. There was also Edward G. Reinhard, author of The Witchery of Wasps (The Century Company, 1929); and John Crompton, who penned The Hunting Wasp (Houghton Mifflin Company, 1955). We also owe a debt of gratitude to the reigning champion of popular entomology, the late Howard Ensign Evans. His masterpiece Wasp Farm (Natural History Press, Doubleday, 1963) remains an inspiration to my own writing and love of the Hymenoptera. Still, Evans is best known for his book Life on a Little-Known Planet (Dutton, 1968), easily the best popular book on insects ever published.

So what does this have to do with Ammophila femurrubra? It means we need another Howard Evans to investigate the biology and behavior of this species. All I was able to determine in my research is that the species ranges in the “southwestern U.S.” How enlightening. My personal observations would tend to reinforce the idea that it is typical of the genus, even “sleeping” in the manner of other Ammophila. It is one of the more common species in urban Tucson, so perhaps it is more adaptable to habitat fragmentation than other species. At about 25 millimeters in length it is of average size for the genus, too.

As always, I encourage all of you to be observant and record your observations if possible. You really never know what you are adding to our collective body of knowledge.

Wednesday, November 3, 2010

I am declaring November as “Ammophila Month,” with the postings on Wednesdays dedicated to different species of this diverse genus of thread-waisted wasps in the family Sphecidae. There are over sixty species in the genus in North America. We’ll start with one of the most spectacular, Ammophila procera, which I was able to photograph near the lighthouse at Cape May Point State Park in New Jersey.

This is not a small wasp, females at least approaching two inches (25-38 mm according to the Bugguide.net page) in length. It ranges across the entire continent from southern Canada to Guatemala. This is the largest species in the eastern U.S. to sport the silver stripes on the side of the thorax, a hallmark of most members of the genus.

I was able to get very close to this female as she was nectaring on goldenrod blossoms, but that is typical of most species of Ammophila. They are solitary, and shy or gentle in nature. They are quite distracted while feeding on nectar, but otherwise very alert and quick to fly. Nesting females are very persistent, however, and if frightened away from a burrow they are excavating will return most of the time to finish it.

Females of Ammophila procera nest in compact sand, so finding this one at the beach on October 15 was not too surprising. The burrow varies from slanted to vertical and ends in a single cell. Once the burrow is completed, the wasp exits, covering the opening and making an orientation flight so she can find it again. Then, off she goes to find a caterpillar.

She will attack a large caterpillar, stinging it into paralysis and then lugging it back to the nest. She grips the caterpillar with her mandibles and middle legs in a manner that seems to render the prey rigid, allowing her to run in a pretty agile manner, all things considered. She can also fly with the caterpillar oriented beneath her body for maximum aerodynamic efficiency. To see one flying with a caterpillar is quite something. The caterpillar often contrasts greatly in color with the wasp, making for an absurd visual unless you know what is going on.

Known host caterpillars for A. procera include caterpillars of the Prominent Moth family Notodontidae such as the White-dotted Prominent Moth, Nadata gibbosa, the Variable Oakleaf Caterpillar, Heterocampa manteo, H. Astarte (no common name), the Morning-glory Prominent, Schizura ipomoeae, members of the genera Datana and Symmerista; and at least one record of the One-eyed Sphinx, Smerinthus cerisyi.

Despite its size and imposing nature, A. procera is not without its own enemies. Among its parasites are “satellite flies” in the family Sarcophagidae, especially Senotainia vigilans and Metopia laterallis. The female flies follow a prey-laden female wasp to her burrow and then look for a chance to lay their own “live” larvae at the mouth of her nest burrow.

You owe it to yourself to see these wasps in action, and I have just the thing to get you hooked on their amazing biology. Dick Walton has shot some amazing videos of this was which can be seen at his websiteDick Walton Natural History Services. The one for the species discussed even includes the satellite flies! Watch for their cameo appearance about midway through the clip.

Have a great week, friends, and remember to tune in again next Wednesday for another installment of “Ammophila Month.”

Monday, November 1, 2010

As I write this there are only 54 shopping days until Christmas. Time for my annual gift recommendations for your naturalist friends (or to add to your own wish list). I won’t even toot my own horn for the Kaufman Field Guide to Insects of North America. Here are three ideas that I am sure will please any “amateur” entomologist out there.

My good friend Daniel Marlos, who started up the website What’sThatBug.com now has a new book to add to his list of successes. The Curious World of Insects: The Bugman’s Guide to the Mysterious and Remarkable Lives of Things That Crawl, a Perigree Book (Penguin Group), has a decidedly whimsical, Victorian-era flavor, in part due to the historical, clip art style illustrations throughout.

Marlos is a visual artist whose interest in insects comes more from a pop culture perspective than an entomological one. Still, Daniel has become a trusted authority in a very short time. He knows Australian insects better than I do, in part because he gets many submissions to his website from that island continent. He is a professor of photography at Los Angeles City College, but is independent of an academic institution when it comes to entomology. This has allowed him to set his own standards for responses to his website users.

Here in his book, he spotlights the insects and related arthropods most frequently encountered and asked about. Daniel’s research skills are first rate, and he excels at interpreting the lives of “bugs” in a way that is both educational and entertaining. It has been my pleasure and delight to see Daniel’s website succeed beyond all expectations; and to see an entomologist and writer metamorphose from such humble beginnings.

Yet another gifted gentleman, Dr. Edward Eric Grissell (Eric to his friends and colleagues), has come out with a much-needed popular book about stinging insects. Bees, Wasps, and Ants: The Indispensable Role of Hymenoptera in Gardens, published by Timber Press in Portland, Oregon, is an outstanding treatment of this fascinating order of insects.

Grissell’s prose is complemented by the jaw-dropping images that illustrate the book. No other popular book still in print communicates the sheer diversity of bees, wasps, sawflies, ants, and related insects in such an eloquent and captivating fashion. This is not a field guide, but is easily the best overview of Hymenoptera for amateur naturalists. Many specimens will be identifiable from the images in this book, but the reader gets a complete understanding of the biology and ecology of the insects as well.

I can’t help but be amused by the endorsement of the book provided by another author, Amy Stewart, who concludes that “Eric Grissell will make a hymenopteran out of all of us.” I, for one, certainly hope not. I enjoy being a human being. Maybe she meant he’ll make a hymenopterist out of all of us.

My final recommendation is a different product that all of us can use: a wall calendar. The Xerces Society presents its 2011 North American Bee Calendar featuring fabulous images of, and pertinent information about, the many solitary bees that pollinate wildflowers and crops across the continent.

The image here shows the cover of the 2010 calendar, but I can hardly wait to get my hands on the new one. Besides getting a superb product, your purchase aids the premiere invertebrate conservation organization in the world.